Compressional wave translating device



April 4, 1961 R. L. PEEK, JR

coMPREssIoNAL WAVE TRANSLATING DEVICE Filed Feb. 22, 1945 /N /E N TOR A.L. PEE/r, JR.

94m JM AHORA/Ey 2,978,670 COMPRESSIONAL WAVE TRANSLATING DEVICE RobertLee Peek, Jr., Short Hills, NJ., assignor to Bell TelephoneLaboratories, Incorporated, New York, N.Y., a corporation of New YorkFiled Feb. 22, 1943, Ser. No. 476,726

9 Claims. (Cl. 340-11) to Vbe exposed to sea water and capable ofefiiciently' transmitting supersonic compressional wave energy, kamagnetostrictive element coupled to the b ase or support member and inenergy communicating relation therewith, means for polarizing themagnetostrictive element i longitudinally, and a signal coilelectromagnetically coupled to the magnetostrictive element. Vibrationof they magnetostrictive element in accordance with energy conveyedthereto through the base or support results in variation in the liuxlinked by the coil and the generation, consequently, of a signal voltagein the coil.A Conversely, when the coil is energized by suitable signalcurrents, the magnetostrictive element elongates and coni tractsaccordingly and drives the base or support to propagate compressionalwaves corresponding to the signals.

In accordance with one feature of this invention, the

magnetostrictive element is in the form Vot' a thin hollow member, forexample, cylindrical, is polarized by a permanent magnet within themember and having its ends or associated pole-pieces in juxtaposition tospaced portions thereof,V and means are provided which in conjunctionwith the magnetostrictive element define a low reluctance path, separatefrom the magnet, for the varying or signal ux.

In accordance with another feature of this invention, the base orsupport and the magnetostrictive element are so constructed and arrangedthat a vibrational node exists adjacent the junction thereof, the signalcoil is mounted adjacent Ythis junction and the magnet, magnetostrictiveelement and, the means defining the low reluctance path with the elementare correlated to maintain a uniform high ux density within themagnetostrictive element adjacent ,the node, so that the flux density inthe region of the node may be maintained at avalue providing opti,-m'urn magnetostrictive action.

The invention and the above noted and other features thereof-Will beunderstood more clearly and fully from the following detaileddescriptionwith reference to theY accompanying drawing in which:

Fig. 1 lis an elevational view in section of a hydrophone illustrativeof one embodiment of-'this invention; and

Fig. 2 is another elevational view in section lcation of the hydrophoneshown in Fig. 1.

Referring now to the drawing, the hydrophone illusof a moditrated inFig. 1, which is suitable for use as a projector this invention, a'

or receiver at supersonic frequencies, for example frequencies of theorder of kilocycles per second, comprises a circular base or support 10of a mold'able insulating material or plastic. clamped to an annularmounting frame 11 by a suitable clamping ring 12, gaskets 13, forexample of soft rubber, being provided between the base or support 10and the frame 11 and clamping ring 12 to Iassure a water-tight sealtherebetween. The frame 11 is axed, as by welding, in water-tightrelation to a housing 14 adapted to be submerged in the sea. Secured tothe mounting frame 11 is a cup-shaped housing 15, for example ofnonmagnetic metal, which has aixed to the Vbase thereof a non-magneticplate16. v

Coaxially arranged with the base or support 10 is a magnetostrictivemember 17, rfor example, of a nickeliron alloy known commercially asPermalloy, Ahaving a f bent end portion 18 embedded in the base orsupport and provided with apertures 19 to allow flow of the base orV Vconstitutes a portion of the bounding wall of a` central recess 21 inthe support or base 10. A bar magnet 22, for example of circularcross-section, extends into the recess 21 in juxtaposition to andcoaxial relation with the;

lip or flange 20 and is supported by an annular pole piece 23 of amaterial having highpermeability secured to the non-magnetic plate 16 asby screws 24, thepole-piece 2.3

having therein an annular recess 25 into which the `magnetostrictivemember 17 projects.

The magnetostrictive member 17 is encompassed by a tubular member 26coaxial with the member 17 and of a magnetic'material having ahighpermeability. The tubular member 26 has a portion 27 of larger diameterin which an annular signal coil 28 is tted and secured, and is supportedfrom the pole-piece 23. The enlarged portion 27 of the tubular member isencompassed by a dish-shaped magnetic member 29 of a material of highkpermeability, a portion of rwhich is embedded in the support or baseland provided with apertures 30 allowing ow of the support or basematerial therethrough during the fabrication of the device. VAs shown inthe drawing, the base ofthe dish-shaped member 29 is in lirm contactwith the base of the end portion 18 of the magnetostrictive element 17.

Advantageously, the base or support 10 and the magnetostrictive member17 are madev of such thickness and length respectively, account beingtaken, of course, of their relative cross sectional dimensions,densities and moduli of elasticity, that the base 10 and member 17vibrate longitudinally as a half wave length resonator,Y

at ya preassigned frequency, with a vibrational node in the element 17adjacent the junction thereof and the base or support 10. 0f course,because of the dilferent materials of which the base and cylinder areconstructed, the absolute magnitude of the ydimensions noted will bedifferent. In the case where the device is intended for operation at asingle frequency, the dimensions noted are related to Ithis frequency.Where the device is intended for operation throughout a band offrequencies, the preassigned frequency is the mean frequency lin thisband.

In the operation of the hydrophone, the magnetostrictive element 17 ispolarized longitudinally by the permanent magnet 22. A direct currentflux is established lalso in the path including the magnet 22, polepiece 23, tubular member 26 and dish-shaped member face of the base 10,the magnetostrictive element 17 is Patented Apr. 4, 1961 This base orsupport is actuated and as a result ofthe varying stresses producedtherein its reluctance varies accordingly and the ux therethrough variesin like manner. The varying component'of-uxows in the-main through-thepatlrcom posed of the magnetostrictive element 17, tubular member 26 anddish-shaped member 29. The -air gaps in this) pathl are of very` smalllength" andy large area? sthat the reluctance thereoffi's smallf Also,-becauseof' 'the` high" permeability of the magnetic memb'ersin'thispath,

the reluctance thereof is small. Hence,` it` will be appreciated thatthere is provided a magnetic loop,=separate from the magnet 22 and ofvery low reluctance, for

the varying hux and a path of high magnetic efliciency for the fluxlinked by the signal: coil 23 is realized. The eddy current losses inthis path are low. Furthermore,

because ofthe relation of the magnet 22 and the lip 20,

a high direct currentux concentration is assuredat the gaptherebetween'and substantially all the'direct current ilux passes to themember 17 by way of the end portion 18 so that a uniform flux densityisestablished inV the portion of member 17 near the base 10, at which themajor stress variations occur. Moreover, because of 'the` relation ofthe thickness of the base and the length of the magnetostrictivecylinder to the wave-length of the signals received, noted heretofore, anode of vibration is established adjacent the junction of these twomembers. This results in the concentration of the' greatest stressvariations in the portion of the magnetostrictive element immediatelyadjacent the signal coil 2S and,

consequently, in the greatest magnetostrictive action in the portion ofthe varying iiux path most closely linked by the coil.

Although the operation of the device has beenL de-` scribed withparticular reference to reception of comv` pressional wave energy, it`will be understood that, as noted heretofore, the device` is `operablealso asa projector and that the several meritorious features pointed outhereinabove `are realized also when the device is operated as aprojector. When the device operates as a projector, signal currents inthe coil 2S result in longi` tudinal vibration of the cylinder 17 whichis communicated to the base 10.

Inasmuch as the base or support 10 isexposed" directly to the sea,problems of obtaining an impedancemtch between the sea and themagnetostrictive element are minimized. Further, inasmuch as" themagnetostrictive, element is supported solely` by the base orsupportan'd the latter is of lightweight material, a vibrating system"of small weight is obtained so that high sensitivityis realized.Further, because-of the small weight noted; the' device shown anddescribed is especially suitable for wide band usage.

The embodiment of this invention illustratedin Fig.' 2 is generallysimilar to that shown in Fig. 1 and described hereinabove. It comprisesthe magnet 22, which is provided with annular pole-pieces 31 and 32 andis sup"- ported upon the base or support 33, which may be of magneticmaterial, by way of anA interposedv pad 34`of resilient material, suchas soft rubber. The magnet and pole-pieces are encompassed by amagnetostrictivecyl-V inder 35, for example, vof Permalloy, one end ofwhich 1s secured in an annular groove 36 inthe base or supporti 33. Themagnetostrictive cylinder 35 is encompassedin turn by a tubular magneticmember 37 of high perme-v ability having an inwardly projecting annularilange-SS terminating adjacent the cylinder 35 and securedltoaresilientpad 39 in turn secured to the basent-support 33-` The signal coil 28encompasses the Vmagneto'strictive cylinder 35 and may be` spacedtherefrom byl a resilient,' e.g. soft rubber sleeve 40. The magnet 22also may be spaced from the magnetostrictive cylinder by a resilient,e.g. soft rubber body 4I.

As in the device shown inFig'. 1,the base or supportv 33 andmagnetostrictive cylinder 35 advantageously have' their thicknessand-length respectively related to a preassignedfrequency so that thebase andcylinder together' vibrate `as' a half wave resonator with anodeadjacent the junction of the base and cylinder. The hydrophoneshown-in-Fig. 2 operates inthesamemanner, as a receiver or projector, asthat illustrated in Fig. 1. Because the magnet 22, tubular member 37, 38and coil 28 are mounted resiliently upon the base or support 33,vibration of these members is negligibly small. The magnetostrictivecylinder 35,' however, being xedly secured to the base or support 33,vibrates` in response to compressional waves" incident upon the base orsupport. Conversely, longitudinal'vibrations ofthef cylinder 35" inresponse' to signal currents in thecoil 28 drivethebase or support 33.

Although specific embodiments of the invention have been shown anddescribed, it will be understood that they are but illustrative and thatvarious' modifications may be made therein without departing from thescope and spirit of this invention as defined in the appended claims.For example, although the base 33 in Fig. 2 has been described as ofmagnetic material, it may bei of aT plastic, yas in Fig. l, and haveimbedded therein a magnetic' elefment` linking the ange 38 tothemagnetostrictive' cylinder 35. n i

What is claimed is:

1. A-compressional wave translating device comprising atubular.magnetostrictive member, meansmfou'nting said member to' allowlongitudinal vibration' thereof, means-for polarizing said memberlongitudinally includ` ing a permanent magnet within said member,Aasignal coil electromagneti'cally coupled to said member, and meansdetining with said member a low reluctance magneticn circuit separatefrom-said magnet, said` last means comprising a tubular magnetic memberof high permeability encompassing said'magnetostri'ctiveV member andmechanically separate therefrom. n

2. A- compressional wave translating device comprising a tubularmagnetostrictive member, means mounting said member for longitudinalvibration, means-for polarizing said member-longitudinally including apermanent magnet encompassed by said member, means defining withsaidmember a low reluctance magnetic circuitseparate from said magnet,said last means comprising a tubular member of low reluctance magneticmaterial encompassing said magnetostrictive member, said tubular memberhaving a portion of extended area immediately` adjacent saidmagnetostrictive `member and llaving also a-portion of greater diameterthan said rst portion, and -a signal coil encompassing saidmagnetostrictive member and positioned within -said portion of greaterdiameter, said magnetostrictive member being vibratile independently-ofsaid tubular member.`

, 3. Acompressional Wave translating device comprising a tubularmagnetostrictivemember, a wave energy responsive support secured to saidmember 'at-one end thereof, means for polarizing said memberlongitudinally including a permanent magnet within said member, havingits poles opposite -the ends thereof and spacedl therefrom and from saidsupport, a signal coil encompassing said member near said one endthereof, andtubular magnetic means encompassing said magnetostrictivemember and having end portions adjacent spaced portions thereof. n i

4. A compressional wave translating device comprising atubular-magnetostrictive member having onen end substantially freelyvibratile and its other endfjoinedto a compressional Awave transmittingmembenmeansl for polarizing said `magnetostrictive member longitudinally`in cluding a magnet encompassed-by saidnflagnetostrictive` member,magnetic meansfat 'opposite' ends of `said-magnetostrictivefmemberextending 4between said magnetand said :magnetostrictive member,Y tubular magnetic: means of low reluctance encompassing saidmagnetostrictive member-and -having end` portions in proximity totheends thereof, and a signal coil rmagnetically linked to said mag-lnetostrictive member.`

5. A compressional vwave translating device comprisinga support adaptedto transmit `compressional wave energy.

apriamo ber encompassing said magnetostrictive member and having aportion of extended area in proximity to the free end portion thereof,means defining a low reluctance magnetic connection between said tubularmember and the fixed end of said magnetostrictive member, and a signallcoil magnetically coupled to said magnetostrictive mem- 6. A'compressional wave translating device comprising a tubularmagnetostrictive member having an inwardly extending ange at oneend'thereo-f, means supporting said member at said one end thereof,means for polarizing said member longitudinally including a magnetwithin said member and having one end in proximity to said ange, apole-piece mounted at the other end of said magnet and extending intoproximity to the other end of said magnetostrictive member, meansdefining with said member a low reluctance magnetic circuit separatefrom said magnet, said last means including a magnetic memberencompassing said magnetostrictive member having a sleeve portion ofextended area in juxtaposition to the end portion of saidmagnetostrictive member nearest said pole-piece and having also atubular portion of greater diameter than said sleeve portion adjacentsaid supporting means, said circuit delining means including also amagnetic vmember engaging said iiange and having a` 4tubular portioncoaxial with and in' juxtaposition to said first tubular portion, and asignal'coil encompassing said magnetostrictive member and supportedwithin said first tubular portion.

7. A compressional wave translating device comprising a support adapted-to transmit compressional wave energy, a tubular` magnetostrictivemember having one end connected to saidv support, means for polarizingsaid member longitudinally including a magnet encompassed by said memberand resiliently mounted on said support, a signal coil magneticallycoupled to said magnetostrictive member, and meansdenmg w1th saldmagnetostrictive member a low reluctance magnetic circuit sep-A aratefrom said magnet, said last means comprising a 6 tubular memberencompassing said magnetostrictive member and resiliently mounted onsaid support.

8. A compressional wave translating device compris-V ing a supportcapable of transmitting compressional wave energy, a tubularmagnetostrictive member having one end fixed to said support, means forpolarizing said magnetostrictive member longitudinally including apermanent magnet within said member, means defining with said member alow reluctance magnetic circuit separate from said magnet, said secondmeans comprising a magnetic Y y, shell having an annular flangeencompassing and adjacent one end of said member and having also atubular. portion encompassing and adjacent the other end of Said member,a signal coil magnetically coupled to said member, 4and means mountingsaid magnet and shell resiliently on said support.

9. A compressional wave translating device comprising a base adapted totransmit compressional wave.

energy, a cylindrical magnetostrictive member having one end fixed tosaid base and its other end free, saidv base member being ofpredetermined thickness and' length `respectively such that said baseand member vibrate together -as a half wave length resonator with a nodein said member adjacent the junction thereof and said base, rmeans for`polarizing said member longitudinally including a magnet Within saidmember, a signal coil adjacent said base and encompassing said member,and means defining with said member a low reluctance magnetic circuitseparatev from said magnet, said last means including tubular magnetic.means enr` compassing said mem-ber, having a portion in proximity tosaid one end thereof ,and-having alsoV a portionof extended areaimmediately adjacent the pcntionfofV said member near said free endthereof. f

' References Cited in the le of this patent 'n UNITED STATES PATENTS

